This invention relates to an improved shrouded propeller tail duct or a "ring tail" assembly for a rotary wing aircraft, particularly a single rotor compound helicopter in which a fixed wing provides lift for high speed forward flight with the rotor unloaded. The shrouded duct within which a rotating propeller is contained provides azimuth and attitude control for the aircraft and controls the direction in which the slipstream from the propeller exits from the shrouded tail duct establishing a transversely directed thrust that counteracts the torque generated by the main lifting rotor and provides aircraft yaw control. The assignee of this application owns a number of patents disclosing various configurations of the "ring tail" or shrouded propeller duct structure in which various configurations of the duct containing the propeller and movable or fixed surfaces control the direction and deflection of the slip stream from the tail propeller. Typical "ring tail" structures developed by the assignee are disclosed in U.S. Pat. Nos. 3,138,349; 3,222,012; 3,241,791 and 3,260,482. All of these disclosures deal with a tail structure having an annular duct containing a forwardly facing propeller which provides thrust for both propelling the aircraft in forward flight and rotor anti-torque and yaw control forces for the aircraft in a slow speed or hovering mode. In general all of these prior art documents disclose various configurations of one or more vertically extending rudder assemblies having a large surface area mounted for pivotal motion about a vertical axis within an annular duct rearwardly of the propeller in which the degree of angular deflection of the rudder surface or surfaces transversely of the duct longitudinal axis and or provisions for modifying the camber of the rudder surface when deflected, control the direction of the propeller slip stream exiting from the rear of the duct to provide both lateral anti torque forces and azimuth directional control forces for the aircraft in all flight conditions.
U.S. Pat. No. 3,260,482, incorporated herein by reference, discloses a "ring tail" structure in which a plurality of vertically extending, multiple section vane assemblies are mounted for pivotal motion about a vertical axis in the duct behind the propeller. The degree of pivotal rotation of each of the vane assemblies between a neutral position in alignment with the axis of the duct and a deflected position extending transversely of the duct axis controls the amount the propeller slip stream is deflected in exiting from the duct to create the transversely directed thrust necessary for counteracting rotor torque and controlling the azimuth direction of the aircraft. This patent also discloses a segment of the inner duct surface on one side of the duct wall supported by a bell crank linkage for bodily movement between a retracted position within a recess in the duct interior surface and an extended position spaced inwardly from the duct wall to protrude angularly transversely across the interior of the duct forwardly of the duct trailing edge in the path of the propeller slip stream.